Two Plymouth lakes were recently removed from the Minnesota Pollution Control Agency’s impaired waters list, following two decades of work to improve the water quality.

Bass and Pomerleau lakes were approved by the U.S. Environmental Protection Agency in April to be removed from the MPCA’s impaired waters list. The delisting represents more than 20 years of effort by the City of Plymouth, lakeshore property owners and the Shingle Creek Watershed Management Commission – the culmination of various projects, practices and programs that have helped improve water quality in the lakes.

The MPCA listed Bass, Pomerleau and Schmidt lakes in Plymouth as impaired in 2002 under the federal Clean Water Act. The three lakes were impaired due to excessive nutrients in the water, including excess phosphorus, which can cause summertime algae blooms that decrease water clarity and limit recreation activities. Schmidt Lake was delisted in 2016.

Strategies for Improving Water Quality in Lakes

When it rains or when snow melts, stormwater runoff flows directly from streets to wetlands and lakes, picking up pollutants and nutrients like phosphorus from sources such as soil erosion and lawn fertilizers. To help mitigate stormwater contaminants, the city added stormwater treatment devices that filter out sediment, leaves, trash and other debris. The city also sweeps streets multiple times per year to reduce contaminants.

As streets near the lakes underwent road construction, rain gardens and other beneficial stormwater management practices were included in the plans to help filter runoff. Additionally, as redevelopment occurred around Pomerleau Lake, Plymouth required properties to incorporate stormwater management practices into the project, improving downstream water quality.

Plymouth also continues to prioritize shoreline restoration – utilizing native plants to reduce erosion while filtering and protecting water bodies from runoff.

Additionally, the City of Plymouth partnered with the local watershed management commission to apply an alum (aluminum sulfate) treatment to the lakes. Alum binds to the phosphorus in the water and settles on the bottom of the lake, preventing the release of additional phosphorus from the sediment in the lakebed. The treatment helps reduce concentrations of nutrients, mitigates algae, increases water clarity, and improves fishing and recreational opportunities for lake users.

For more information about the city’s environmental stewardship efforts, visit plymouthmn.gov/environment.